quick question, i just got some nb 240's, came with ceramic pyramid spikes. After one 8k xc race the spikes are worn down. Are there any benefits for me running with ceramic spikes vs. metal spikes in xc besides weight? Are they less likely to cause injury and fatigue on your body? My coach has the old school metal spikes for us, should I just use these instead of purchasing enough ceramics to last through xc season?